I agree that John's gospel is written so that a Christian's joy may be full. A Christian can be in fellowship with God or out of fellowship. They can sin and they can not sin. I don't want to say "sin you will and sin you must" I agree that we should be idealistic about the idea that we can not sin, but this idealism isn't absolute.
Rom 7 I think talks both of the unbeliever who has no experience with God and the believer who is struggling. There are too many times where Paul uses the 1 person personak pronoun, "the good that I do", that "which I do". If this were just a hypothetical struggle Paul would have used the past tense or would have referred to another person, not himself.
I recognize that there are scholars on both sides of the issue about Rom. 7, it is too much to say that one is a heretic if they don't believe like you do. One side may overemphasize the struggle, but you are definitely de-emphasizing it.
The wretched man of Romans 7 is not confusing in the slightest. The only reason it causes confusion is because people are trying to fit it into their theology.
Paul is using a grammatical technique called the "historical present." It is a technique used to give emphasis to a point being made. We use this technique in English and it is found quite commonly in ancient Greek literature.
Historical present - Wikipedia, the free encyclopedia
http://apaclassics.org/sites/default/files/documents/abstracts/george_1.pdf
If Paul is literally speaking of Himself in the present tense, as a faithful Christian, then that means that salvation leaves one "carnal and sold under sin" which would be a complete contradiction of what Paul writes in Chapter 6 and 8 of Romans. The Bible is a harmonious whole not a book of isolated passages and verses to be proof texted.
Do you really believe that Jesus came to save us from our sins (Mat 1:21), set us free indeed (Joh 8:36), to redeem us from all iniquity and make us pure (Tit 2:14) and leave us as wretches who are carnal and sold under sin?
Sinners are held captive to their sin. The Gospel effects a release from captivity. It is to deny the Gospel to preach a salvation IN sin. It is to deny the power of God to teach that God's salvation leaves one a wretch, carnal and enslaved to sin.
There is no possible way for any person who has genuinely escaped the corruption that is in the world through lust, via dying to sin and putting on the mind of Christ, to believe that Paul is teaching that Christian's are wretches. You won't find any of the early church writers presenting the wretched man of Romans 7 as the present Christian walk. That notion was borne out of the introduction of "inability" into Christian doctrine via Augustine of Hippo in the Fourth Century. Augustinian theology disconnects the actual condition of the heart from salvation and thus by necessity teaches that one can be in a wretched state and saved at the same time.